This disclosure relates to a methodology and systems for designing a broach tool used to machine components such as rotating disks used in aerospace applications.
A gas turbine engine integrates a compressor and a turbine having components that rotate at high speeds, which subject the components to significant centrifugal loading during operations. One component that rotates at high speeds is a disk that carries multiple circumferentially arranged blades. The blades are commonly attached at an outer circumference of the disk through respective blade attachment slots. Each of the slots has a profile that corresponds with the root of the blade, and has a configuration designed to retain the blade in the slot during operation. The blade attachments slots are generally of a “fir-tree” configuration to increase the load bearing surface area of the disk. Broaching is a technique often utilized for forming fir-tree slots in gas turbine engine disks.
In at least some known broaching processes, a broach tool includes a series of cutting teeth formed on a single solid bar or insert. The inserts and teeth are pulled through a workpiece to gradually remove material and form the desired slot opening. Each cutting tooth is typically slightly different from the adjacent cutting teeth. The fir-tree slots are generally formed in a three-stage broaching operation. Each stage may employ a broach tool including a set of up to thirty or more inserts. A rough shape of the slot is generally formed during an initial rough broaching stage. An intermediate broaching stage is used to form the intermediate shape of the slot. Finally, a finishing broaching stage is generally used to form the profile of the fir-tree slot.
Several known design approaches have disclosed fir-treelbroach slot configurations and details of the geometric assimilation of lines, arcs, and angles for the purposes of reducing centrifugal forces, bending moments, and vibrations and the consequential peak stresses that result at the attachment points. However, the limitations of such known broaching processes that are associated with aerospace materials include excessive material strain hardening, surface microstructure alteration (such as white etched layer and bend microstructures), slot deformation, and ripple formation on the slot surfaces. The ripples and defects on the slot surfaces may lead to a decreased disk life because of fretting between the blade root and the disk surface during engine operation. In addition to the high cost of the broach tools and limited tool life, the design of known broach tools is based on tribunal knowledge of other materials. These known design methods result in high scrap rate and lower tool life because of the surface anomalies generated during finishing of the slot. Such part scrap rate is generally higher compared to other machining processes due to a compromised surface integrity if the broach tool is not designed properly to account for the progress of strain hardening during machining.
What is needed is an approach and system for designing broach tools that facilitate reducing the undesirable effects of known broach design methods and systems.